Help! 1991 L98 runs fine cold dies out

[stratinik]

i recently purchased a 91 L98 , six speed. has 21,000 miles. runs fine when cold, after 15 minutes, begins knocking sound,,after 5 more minutes, dies out. throws no code,,next day starts right up does same thing. eng temp normal as are all other gauges, replaced EGR, cap, rotor, ingition module.,.someone looked at it said belived was catalytic converter....would cats cause that? should i try MAP sensor or EGR solenoid first? any help appreciated. thanks

 

[Schrade]

i recently purchased a 91 L98 , six speed. has 21,000 miles. runs fine when cold, after 15 minutes, begins knocking sound,,after 5 more minutes, dies out. throws no code,,next day starts right up does same thing. eng temp normal as are all other gauges, replaced EGR, cap, rotor, ingition module.,.someone looked at it said belived was catalytic converter....would cats cause that? should i try MAP sensor or EGR solenoid first? any help appreciated. thanks

Why did someone think it was the cat convertor? Did they give any reason? Or maybe it was just a meaningless guess? People say stuff that means nothin - including mechanics yup. Ask if they think it might be the air freshener needs replacement...

EVERY engine runs PERFECT when cold. Warmed up, closed loop is the only way to see what's up.

The knocking sound is what we gotta' key on right now. EXACTLY where is it coming from? IF AND ONLY IF NEAR THE TRANNY/MOTOR BELLHOUSING AREA, does it do it with the clutch pedal depressed?

A knocking sound should be caught by the anti-knock sensor, and it should retard the timing. AND, when it continues, the computer reads the amount of time it has to retard the timing, and after so long x-minutes, it flips the bird. Just kidding - it flips a code for timing retarded too long. This MIGHT only show as a H history code, not C current code.

Get a paper clip in the ALDL and get a pencil ready...

 

[vetteboy86]

That sounds like a strange situation to me. Where does it sound like it is coming from? Top end of the motor, front, back? I know it is hard to determine.

 

[tmkassin]

Switch your temp gage to didital and watch it. See if you can detect when the thermostat is opening. The temp should climb till it opens then dip. If the thermostat is stuck the temp will continue to climb...You can't always trust the analog gages.